“IS-LMentary”

The IS-LM model is one of the central tenants of the neoclassical movement and shows the relationship between interest rates, the real outcome, the market for goods and services, and the money market. It is one of the basic tools to know the economic policy and for that reason it is a necessary concept of macroeconomics. The X axis represents the level of income Y (or GDP of a country), and the Y axis represents the interest rate (r) of that country. The IS curve denotes all of the equilibrium points in the goods and services market and is named after the terms investment and savings. The LM curve represents all of the equilibrium points in the money market and owes its name to L (liquidity) and M (money supply). The intersection of both curves constitutes the moment of “equilibrium”, where there is a simultaneous balance in both markets. It should be noted that the IS-LM model is an instrument for the static analysis of the economy and it constitutes a valuable tool of economic policy, or more simply, fiscal and monetary policy (Mankiw, 330).

The LM curve represents all points at which the various combinations of interest rate and real money market income levels are in equilibrium. Its positive slope reflects the role of money in the economy in a simple way: a high interest rate encourages investment, which stimulates income (GDP) and its shift to the right. On the other hand, a low interest rate discourages investment and causes firms and individuals to opt for large amounts of cash (preference for liquidity), which causes a decrease in income. In extreme circumstances, interest rates become so low that the preference for liquidity becomes a liquidity trap (Mankiw, 333-335). The LM curve is defined by:

M/P = L(r,Y)

M/P represents the real money quantity, where M is the nominal money amount and P is the price level. L is the real demand for money, which is a function of the interest rate (r) and the real GDP or income (Y). As with the IS curve, each point on the LM curve represents a situation of equilibrium in the money market. This includes the need to maintain cash for everyday transactions. As Krugman mentions, the concept of the liquidity trap appears when “nominal interest rates reach a minimum level below which they cannot be reduced, so that monetary policy ceases to be effective as an instrument of expansion of aggregate demand” (Krugman, 1).